5,273 research outputs found

    Interface effects in d-wave superconductor-ferromagnet junctions

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    Measurements of the differential conductance spectra of YBa2Cu3O7-SrRuO3 and YBa2Cu3O7-La0.67Ca_0.33MnO3 ramp-type junctions along the node and anti-node directions are reported. The results are consistent with a crossed Andreev reflection effect only in YBa2Cu3O7-SrRuO3 junctions where the domain wall width of SrRuO3 is comparable with the coherence length of YBa2Cu3O7. No such effect was observed in the YBa2Cu3O7-La0.67Ca0.33MnO3 junctions, which is in line with the much larger (x10) domain wall width of La0.67Ca0.33MnO3. We also show that crossed Andreev exists only in the anti-node direction. Furthermore, we find evidence that crossed Andreev in YBa2Cu3O7 junctions is not sensitive to nm-scale interface defects, suggesting that the length scale of the crossed Andreev effect is larger than the coherence length, but still smaller than the La0.67Ca0.33MnO3's domain wall width.Comment: 5 pages, 6 figure

    Quantum vortex tunneling in YBa2Cu3O7βˆ’Ξ΄YBa_2Cu_3O_{7-\delta} thin films

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    Cuprate films offer a unique opportunity to observe vortex tunneling effects, due to their unusually low superfluid density and short coherence length. Here, we measure the magnetoresistance (\textit{MR}) due to vortex motion of a long meander line of a superconducting film made of underdoped YBa2Cu3O7βˆ’Ξ΄YBa_2Cu_3O_{7-\delta}. At low temperatures (\textit{T}), the \textit{MR} shows a significant deviation from Arrhenius activation. The data is consistent with two dimensional Variable Range Hopping (VRH) of single vortices, i.e. MR∝exp[βˆ’(T0/T)1/3]MR\propto exp[-(T_0/T)^{1/3}]. The VRH temperature scale T0T_0 depends on the vortex tunneling rates between pinning sites. We discuss its magnitude with respect to estimated parameters of the meander thin film.Comment: 5 figure

    A study of the ferromagnetic transition of SrRuO3SrRuO_3 in nanometer thick bilayers with YBa2Cu3OyYBa_2Cu_3O_y, La1.88Sr0.12CuO4βˆ’yLa_{1.88}Sr_{0.12}CuO_{4-y}, Au and Cr: Signature of injected carriers in the pseudogap regime

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    The hypothesis regarding the existence of uncorrelated pre-formed pairs in the pseudogap regime of superconducting YBa2Cu3OyYBa_2Cu_3O_y is tested experimentally using bilayers of YBa2Cu3OyYBa_2Cu_3O_y and the itinerant ferromagnet SrRuO3SrRuO_3. In our study, we monitor the influence of YBa2Cu3OyYBa_2Cu_3O_y on TpT_p, the ferromagnetic ordering temperature of SrRuO3SrRuO_3. Here, TpT_p is the temperature of maximum dM/dT or dR/dT where M and R are the magnetization and resistance of SrRuO3SrRuO_3, respectively. We compare the results with similar measurements carried out on bilayers of La1.88Sr0.12CuO4βˆ’yLa_{1.88}Sr_{0.12}CuO_{4-y}, AuAu and CrCr with SrRuO3SrRuO_3. We find that in bilayers made of underdoped 10 nm YBa2Cu3OyYBa_2Cu_3O_y/5 nm SrRuO3SrRuO_3, the TpT_p values are shifted to lower temperatures by up to 6-8 K as compared to Tpβ‰ˆ140T_p\approx 140 K of the 5 nm thick reference SrRuO3SrRuO_3 film. In contrast, in the other type of bilayers, which are not in the pseudogap regime near TpT_p, only a smaller shift of up to Β±\pm2 K is observed. These differences are discussed in terms of a proximity effect, where carriers from the YBa2Cu3OyYBa_2Cu_3O_y layer are injected into the SrRuO3SrRuO_3 layer and vice versa. We suggest that correlated electrons in the pseudogap regime of YBa2Cu3OyYBa_2Cu_3O_y are responsible for the observed large TpT_p shifts.Comment: 9 figure

    Transport and spectroscopic properties of superconductor - ferromagnet - superconductor junctions of La1.9Sr0.1CuO4La_{1.9}Sr_{0.1}CuO_4 - La0.67Ca0.33MnO3La_{0.67}Ca_{0.33}MnO_3 - La1.9Sr0.1CuO4La_{1.9}Sr_{0.1}CuO_4

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    Transport and Conductance spectra measurements of ramp-type junctions made of cuprate superconducting La1.9Sr0.1CuO4La_{1.9}Sr_{0.1}CuO_4 electrodes and a manganite ferromagnetic La0.67Ca0.33MnO3La_{0.67}Ca_{0.33}MnO_3 barrier are reported. At low temperatures below TcT_c, the conductance spectra show Andreev-like broad peaks superposed on a tunneling-like background, and sometimes also sub-gap Andreev resonances. The energy gap values Ξ”\Delta found from fits of the data ranged mostly between 7-10 mV. As usual, the gap features were suppressed under magnetic fields but revealed the tunneling-like conductance background. After field cycling to 5 or 6 T and back to 0 T, the conductance spectra were always higher than under zero field cooling, reflecting the negative magnetoresistance of the manganite barrier. A signature of superparamagnetism was found in the conductance spectra of junctions with a 12 nm thick LCMO barrier. Observed critical currents with barrier thickness of 12 nm or more, were shown to be an artifact due to incomplete milling of one of the superconducting electrodes.Comment: 10 figure
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